EP patent application 0 281 252 and corresponding U.S. Pat. No. 4,867,792 disclose a thixotropic tire balancing composition having a yield stress value between 30 Pa and 260 Pa being capable of balancing tires by being able to flow under the influence of the vibrations induced when a heavy spot on the tire hits the road surface. The balancing composition distributes itself in a wheel assembly consisting of a tire mounted on a rim and having a heavy spot.
DE patent application 3823926 discloses a method and an apparatus for the analysis of production-dependent, circumferentially distributed non-uniformities of a vehicle tire, wherein a predetermined non-uniformity is analyzed by successively mounting a plurality of tires on the measuring rim in each case with the point having the non-uniformities to be analyzed in the same respective angular rotation position, storing the magnitudes of the non-uniformities of each tire measured around its circumference and adding them up. The method is suitable, inter alia, for the quality control of motor vehicle tires.
U.S. Pat. No. 5,431,726 discloses a tire gel balancing composition having a Storage modulus of between 3000 and 15000 Pa and a Specific Gravity less than 1000 kg/m3 in the temperature range between −20° C. and +90° C. and being capable of balancing tires by being able to flow under the vibrations caused by imbalance in a wheel assembly.
PCT patent application WO 98/52009 and corresponding DE patent application 197 19 886 disclose a method for balancing automobile wheel assemblies comprising pneumatic tires, comprising introducing a viscous balancing composition into the tire; mounting the wheel on a rotatable assembly; pressing a rotatable drum and the tread surface of the wheel in the rotatable assembly against one another with a static force F, the axes of rotation of the drum and the wheel assembly being essentially parallel; and driving the drum and/or the wheel assembly to rotation for a time period T; the force F and the time T being sufficient to cause the balancing composition to be distributed inside the tire, thereby balancing the wheel assembly. The method may preferably be carried out on an apparatus comprising a rotatable assembly on which a wheel assembly comprising a rim and a pneumatic tire may be mounted; a rotatably mounted drum having an axis of rotation essentially parallel to that of the rotatable wheel assembly, the axes drum and/or the rotatable wheel assembly being capable of being moved in a direction towards and away from one another; driving means for rotating the rotatable wheel assembly and/or the drum; spring means and dampening means for providing static force and dampening in a direction between the axes of rotation of the drum and the rotatable wheel assembly, respectively, and essentially at right angles to said axes; and spring means and/or dampening means mounted between the axis of rotation of the rotatable wheel assembly and the ground and/or between the axis of rotation of the drum and the ground.
DE patent application 198 57 646 discloses a method for balancing tires by introducing a balancing substance inside the tire, comprising placing a substance with definite properties, shape, geometry and weight inside the tire; and moving to the point of imbalance by rotating the tire. The method may also be used for balancing other rotating objects.
DE patent application 198 53 691 discloses a method for introducing tire-balancing substance as internal circumferential gel bead. The substance characteristic, shape, weight, geometry and its deposition locations are defined. The internal surface of the tire exhibits defined shape and geometry. One or more endless strands may be employed. Strand cross section may be circular, semicircular, flattened, triangular, quadrilateral or polygonal. The one or more strands are distributed over the entire circumference, or just part of it, or both types of distribution take place. Strand portions are applied opposite the valve, when mounted on the rim. They are applied at or away from the equatorial plane, symmetrically, or else asymmetrically. The substance is injected through the valve in set quantity. A gel with a defined viscosity, thixotropy, long term stability, and compatibility with the tire's inner surface is used. The tire has one or more circumferential grooves, optionally between beads, to accept the substance.
DE patent application 199 16 564 discloses a method and an apparatus for distributing weights in tires, involving applying weight material to the inner liners of tires. Tire inhomogeneity is measured on a conventional machine before the tire is on the rim and the measurement values are fed to a computer, which determines the quantity of weight material to be applied and where to apply it to compensate the inhomogeneity and which is coupled to a machine for applying weight material to the required place in the required quantity.
A viscous, for example thixotropic, balancing substance, for example composition, may be used for balancing a vehicle wheel comprising a tire. The balancing substance may be inserted into the tire before the tire is mounted to a rim, or through a valve. For balancing the vehicle wheel, the substance may be distributed by driving a vehicle comprising the vehicle wheel, or mounting the vehicle wheel on a rotatable assembly; pressing a rotatable drum and a tread surface of the vehicle wheel in the rotatable assembly against one another with a static force; and driving the drum and/or the vehicle wheel to rotation for a time period; the force and the time being sufficient to cause the balancing composition to be distributed inside the tire, thereby balancing the vehicle wheel.
Driving experience of a vehicle is determined, among other factors, by surface quality of the road and quality, e.g. homogeneity or uniformity, of the vehicle's wheels. A vehicle wheel is a system comprising a tire, a rim and a valve. Non-uniformity or inhomogeneity of the vehicle wheel may result from an uneven mass distribution, i.e. unbalance, of a tire or a rim or both, a geometrical abnormality, for example axial run-out or radial run-out or both, of the tire or the rim or both, or a variation in axial, radial or tangential stiffness (axial-force fluctuation, radial-force fluctuation, tangential-force fluctuation) of the tire or the rim or both, or off-centre mounting of the tire on the rim or the rim on a vehicle's axle or both. While some types of non-uniformities, for example resulting from an overlap of material or a valve hole, are intentional, others, for example resulting from uneven distances and densities of cord fabrics, i.e. threads, during production, subsidence behavior during mounting or flat spots owing to thermoplastic behavior after driving, are unintentional. Thus, balancing the wheel improves the driving experience, as it compensates for the uneven mass distribution, but not the variations in stiffness.
If the tire is according to its specification and, thus, does not have a significant geometrical abnormality, such as axial run-out or radial run-out, or significant variations in axial, radial or tangential stiffness, the balanced vehicle wheel provides, from a subjective view, for a comfortable driving experience.
However, vehicle manufactures and also repair shops need a method, an apparatus and a system for efficiently, and preferably predominantly automatically, analyzing whether a vehicle wheel comprising a tire and a thixotropic balancing substance is balanced, or determining a residual unbalance of the vehicle wheel.
Conventional methods, apparatuses and systems for analyzing conventional vehicle wheels, i.e. vehicle wheels balanced with metal, e.g. zinc, weights, without load cannot be used for efficiently analyzing a vehicle wheel comprising a tire and a thixotropic balancing substance.
For these and other reasons, there is a need for the invention as set forth in the following in the embodiments.